Devices operating on principles similar to the present invention have been known and used heretofore. Known prior art concerned is described in U.S. Pat. No. 3,757,122, granted to Bossen, et al; number U.S. Pat. No. 2,968,729, Pepper, et al; U.S. Pat. No. 3,889,121, Bossen; U.S. Pat. No. 3,761,712, Listerman; U.S. Pat. No. 3,121,166, Vossberg; U.S. Pat. No. 4,147,931, Puumalainen; U.S. Pat. No. 4,037,104, Allport; and U.S. Pat. No. 4,301,366, Bertin, et al.
The Basis Weight Gauging Apparatus, System and Method of Bossen, et al, '122, utilizes a fixed immobile installation having separate heads for radiating and detecting with a spaced relationship therebetween, and requires that a prior measurement of a representative sample of the material be supplied. This non-portable device makes no provision for measuring and/or compensating for the distance between radiating/detecting heads and the material.
The device of Pepper, et al, '729, also requires the use of a representative sample of the material being measured. This device further requires the use of two ionization chambers, together with a bi-directional emissivity pattern of the radiating material, one lobe of which is constantly irradiating the sample as a reference standard. A difference-derived signal is employed to drive a motor which varies an aperture controlling the amount of radiation applied to the material being measured. A mechanically coupled gauge provides an indication of the thickness/density of the material. It would appear that this device would not be well-adapted for portability, and there is no provision for measuring and/or compensating for the distance between radiating/detecting heads and the material.
The device described by Bossen in U.S. Pat. No. 3,889,121 utilizes beta and X-Ray radiating materials but is expressly designed for the particular situation of its described embodiment, wherein a core made of a specific material, such as steel, is overlaid with a dissimilar material, such as rubber. This device must also be calibrated with a series of representative samples of the material(s) to be measured. There is no provision made for measuring and/or compensating for the distance between the radiating/detecting heads and the material. Bossen's claims are for: "1. An apparatus for measuring the weight per unit area of various constituents of a tire fabric manufactured by calendering rubber onto both sides of a metal cord, comprising. . . ", and "9. Apparatus for measuring the weight per unit area of a manufactured sheet product consisting of a first material layer having a first scattering or absorption characteristic and a second material layer having a second scattering or absorption characteristic and wherein said first characteristic is different from said second characteristic, said apparatus comprising:. . . ". The limitations of a tire fabric and first and second material layers clearly distinguish this device from that of the present invention which is generally intended for all types of sheet materials.
The device of Listerman, '712, although utilizing a source for both neutron and gamma radiation, is for a moisture gauge to determine the moisture content of bulk substances and not a density/thickness measurement device.
The non-portable device of Vossberg, '166, designed and intended for use particularly in measuring the volumetric contents of a series of sealed cans, has no provision for measuring and/or compensating for the distance between the radiating/detecting heads and the material. His claim is for a method of alternating between two sources or power levels of radiation to irradiate one side of a specimen to be measured.
Puumalainen, '931, teaches a device for measuring the unit area weight of a coating on paper by first coating it with a pre-coat. This device is said by its inventor to require 10-20 seconds to achieve a measuring accuracy of +0.5 grams per square meter. This would appear to impose a severe limitation on the possible flow rate of the material to be measured. Further, this device does not directly indicate any weights but only provides an indication from which the weight of the coating is calculated.
Allport, '104, teaches a device for measuring the thickness of ferrous and nonferrous metals, specifically. This device uses radiation sources on one side of the material and detectors on the other side, requiring that both sides of the material be accessible. Allport's purpose in this invention is to compensate for changes in the composition of a sheet of metal alloy without affecting the usefulness of the device to monitor the thickness thereof.
The device of Bertin, et al, '366, is designed to detect a special kind of thickness variation, called "chatter," which is peculiar to cold rolled steel.
The devices just described above encompass many applications of the art of measuring sheet materials through the use of radioactive emissions and the reflections thereof. However, such prior art devices have failed to provide a backscatter gauge which is portable and usable under unlimited environmental conditions, and wherein only one side of the material to be measured must be accessible. Furthermore, such prior art devices have been subject to errors introduced by such factors as movement of the material being measured, obscuration of emissivity windows, aging of the radioactivity emitters, etc.
Accordingly, it is a principal object of the present invention to provide an improved basis weight measurement system utilizing any of a variety of devices which can make such measurements without the need for direct contact with the material being measured.
It is another object of the present invention to provide such an improved basis weight measurement system utilizing devices which can make such measurements without being affected by movement of the material being measured.
It is a further object of the present invention to provide such a basis weight measurement system utilizing devices which may be used in either fixed immobile, fixed mobile (scanning), or portable applications.
It is still another object of the present invention to provide such a basis weight measurement system utilizing devices which can employ any combination of alpha, beta, gamma, and/or X-Ray radiation, or high and low power combinations of such radiation emitters to effect such measurements.
It is yet a further object of the present invention to provide such a basis weight measurement system utilizing devices which will supply identification data to uniquely and individually identify each measurement made.
It is still another object of the present invention to provide a such a basis weight measurement system utilizing devices which can be substantially self-calibrating.
These and other objects and advantages of the present invention will become readily apparent from the following detailed description, when taken together with the accompanying drawings.